vintage variac and auto-transformers

Discussion in '"Boat Anchor" & Classic Equipment' started by KM4HNF, Jan 19, 2019.

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  1. KM4HNF

    KM4HNF Ham Member QRZ Page

    I have two pieces of vintage equipment, a Variac W5MT Autotransformer from General Radio USA, and a RCA TV. ISOTAP WP-25A ISOLATION TRANSFORMER.

    Both have two-prong plugs, and need new cords. Should they both be changed to polarized two-prong plugs or three prong plugs. If so, would a green ground wire be bolted to the metal cases? Or should I just change cords and reuse the existing plugs?

    Simple question, I guess, but wanted suggestions so I only have to do it once.

  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    I would go with the 3-wire cord and attach the green ("ground") wire to the cabinets / cases. That would add several levels of protection to the variacs.

    Glen, K9STH
    WA7PRC and N2EY like this.
  3. KM4HNF

    KM4HNF Ham Member QRZ Page

    agreed thanks Glen
  4. W9GB

    W9GB Ham Member QRZ Page

    RJ -
    The NEMA 1-15R (two-prong) Snap-In receptacle can be acquired from Leviton.
    Dimension specifications, below.
    The OLD part number was 298-x (Where “x” was color, W for White, Brown & Black)
    See eBay auction # 232074774701 for 298-W

    Current Production
    Leviton 1306-W (Polarized, White Color, used in appliance mfg., primarily stoves)

    RCA ISO-TAP WP-25A Isolation Transformer
    Later models, after 1965 NEC, featured NEMA 5-15R for DIRECT and
    NEMA 1-15R (Unpolarized OR Polarized)

    517E1288-14DE-4066-97D5-A17B78417A36.png 76BF347E-72BB-43FB-8C9E-F64455C50F30.jpeg

    Mark Palmer, Antique Radio Forum provided these Resustance Readings
    for a functional RCA WP-25A:
    Direct: High 1.17 ohms, Med 1.02, Low 0.93
    Isolated: High 1.83 ohms, Med 1.39, Low 1.25
    Last edited: Feb 9, 2019
  5. W9GB

    W9GB Ham Member QRZ Page

    Qualtek Electronics Corp. of Mentor, OH (USA distributor of Rong Feng Industrial, Taiwan)
    is another supplier for replacement AC outlets.

    The NEMA 5-15R come in a variety of terminations (and different panel cutouts).
    Solder or IDC style have square cut-outs.
    Earlier versions of the RCA WP-25A featured the usage of Despard Receptacles.
    Despard switches (toggle from left to right) and NEMA 1-15R receptacles were manufactured by Leviton, Bryant, Sierra, Pass & Seymour and others in 1950s and 1960s.
    NEC changes in 1962, 1965, and 1970 limited the usage of this style to switches. Sierra Electric, a major mfg. of this style, closed operations in 1990s.
    Pass-Seymour designed a NEMA 5-15R outlet to fit this form factor — BUT not cheap ($19.95).

    You can find replacement Despard light switches, power outlets, and pilot lights for updating or repairs at Kyle Switch Plates.
    Last edited: Feb 9, 2019
  6. KE0ZU

    KE0ZU Ham Member QRZ Page

    The RCA was originally designed to be "safe" and looking at the schematic, there are no grounds anywhere in sight. I'd leave them that way and replace with "original equipment" type cords.
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    My 280V/10A Superior Electric Powerstat™ came to me w/o any connectors. It has only a terminal block. I added NEMA 6 connectors on the ends of some SO cord, with the ground wires connected to the Powerstat's metal frame. :)
  8. KX4OM

    KX4OM Ham Member QRZ Page

    Mine came from an old washing machine out on the curb back in '75 in Highlands NJ, and it was probably 25 years old then. I still use it.

    Ted, KX4OM
  9. KM4HNF

    KM4HNF Ham Member QRZ Page

    Thank you all for that wealth of info. The one I have is identical to the "blue" one shown toward the bottom of the page, just above the Pass-Seymour receptacle.
    It seems to be working fine though, was just considering new cord.
  10. AA5CT

    AA5CT Ham Member QRZ Page

    re: "Both have two-prong plugs, and need new cords. Should they both be changed to polarized two-prong plugs or three prong plugs. If so, would a green ground wire be bolted to the metal cases?"

    Do you work in a basement, on a sometimes wet or damp concrete floor? Could be a floor in the garage or a basement ...

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